Organic light emitting display and driving method thereof

ABSTRACT

An organic light emitting diode (OLED) display comprises: an OLED; a driving transistor for supplying driving current to the OLED; a data line for transmitting a corresponding data signal to the driving transistor; a first transistor having a first electrode connected to one electrode of the OLED and a second electrode connected to the data line; and a second transistor having a first electrode connected to the data line and a second electrode connected a gate electrode of the driving transistor, wherein the first transistor, the second transistor, and the driving transistor are turned on, a first current and a second current are respectively sunk in a path of driving current from the driving transistor to the OLED through the data line, and a threshold voltage and mobility of the driving transistor are calculated by receiving a first voltage and a second voltage applied to the gate electrode of the driving transistor corresponding to sinking of the first current and the second current through the second transistor and the data line, and the data signal transmitted to the data line is compensated.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationearlier filed in the Korean Intellectual Property Office on Feb. 23,2010 and there duly assigned Serial No. 10-2010-0016383.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting diode (OLED)display and a driving method thereof. More particularly, the presentinvention relates to an organic light emitting diode display for quicklycompensating deterioration of an organic light emitting diode anddisplaying an image with uniform luminance irrespective of a thresholdvoltage and mobility of a driving transistor, and a driving methodthereof.

2. Description of the Related Art

Various kinds of flat display devices that are capable of reducingdetriments of cathode ray tubes (CRT), such as their heavy weight andlarge size, have been developed in recent years. Such flat displaydevices include liquid crystal displays (LCDs), field emission displays(FEDs), plasma display panels (PDPs), and organic light emitting diode(OLED) displays.

Among the above flat panel displays, the OLED display using an organiclight emitting diode generating light by a recombination of electronsand holes for the display of images has a fast response speed, is drivenwith low power consumption, and has excellent luminous efficiency,luminance, and viewing angle such that it has been spotlighted.

Generally, the organic light emitting diode display is classified into apassive matrix organic light emitting diode (PMOLED) and an activematrix organic light emitting diode (AMOLED) according to a drivingmethod of the organic light emitting diode.

The passive matrix uses a method in which an anode and a cathode areformed to cross each other and cathode lines and anode lines areselectively driven, and the active matrix uses a method in which a thinfilm transistor and a capacitor are integrated in each pixel and avoltage is maintained by a capacitor. The passive matrix type has thesimple structure and a low cost, however it is difficult to realize apanel of a large size or high accuracy. In contrast, with the activematrix type it is possible to realize a panel of a large size or highaccuracy, however it is difficult to technically realize the controlmethod thereof and a comparatively high cost is required.

In an aspect of resolution, contrast, and operation speed, the currenttrend is toward the active matrix organic light emitting diode (AMOLED)display where respective unit pixels selectively turn on or off.

However, the luminous efficiency is decreased by deterioration of theorganic light emitting diode (OLED) such that the light emittingluminance is decreased for the same current.

Also, the current flowing in the organic light emitting diode accordingto the same data signal is changed by non-uniformity of the thresholdvoltage of the driving transistor controlling the current flowing in theorganic light emitting diode and a deviation of the electron mobility.

The deterioration of the organic light emitting diode results in imagesticking, and the characteristic deviation of the driving transistorresults in mura.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide an organiclight emitting diode (OLED) display for improving image quality bypreventing non-uniformity and deviation of luminance caused bynon-uniformity of threshold voltages of transistors of pixels of theorganic light emitting diode display and deviation of electron mobility,and a driving method thereof.

The present invention has been made in another effort to provide anorganic light emitting diode display for realizing desired luminanceirrespective of deterioration of an organic light emitting diode inreal-time and by quickly sensing deterioration of the organic lightemitting diode included in pixels of the organic light emitting diodedisplay, and a driving method thereof.

The technical objects of the present invention are not limited by theabove technical objects, and other technical objects that are notmentioned will be apparently understood by a person of ordinary skill inthe art from the following description.

An exemplary embodiment of the present invention provides an organiclight emitting diode display comprising: an organic light emittingdiode; a driving transistor for supplying driving current to the organiclight emitting diode; a data line for transmitting a corresponding datasignal to the driving transistor; a first transistor having a firstelectrode connected to one electrode of the organic light emitting diodeand a second electrode connected to the data line; and a secondtransistor having a first electrode connected to the data line and asecond electrode connected to a gate electrode of the drivingtransistor.

The first transistor, the second transistor, and the driving transistorare turned on, and a first current and a second current are respectivelysunk in a path of a driving current from the driving transistor to theorganic light emitting diode through the data line.

A threshold voltage and an electron mobility of the driving transistorare calculated by receiving a first voltage and a second voltage appliedto the gate electrode of the driving transistor corresponding to sinkingof the first current and the second current through the secondtransistor and the data line, and the data signal transmitted to thedata line is compensated.

The display receives a third voltage applied to one electrode of theorganic light emitting diode through the data line while supplying apredetermined third current to the organic light emitting diode byturning on the first transistor.

The display detects a deterioration degree of the organic light emittingdiode according to the third voltage, and compensates a data signaltransmitted to the data line in order to compensate the detecteddeterioration.

The organic light emitting diode display further comprises: acompensator for receiving the third voltage through the data line; and acompensator selecting switch provided between the data line and thecompensator, and transmitting the third voltage to the compensator whenturned on by a corresponding selection signal.

The compensator comprises a current source for supplying a third currentso as to detect the third voltage.

The compensator further comprises a controller for determining adeterioration degree of the organic light emitting diode according tothe third voltage, and determining a compensation amount of the datasignal according to the determined deterioration degree.

The second current has a current value that is less than that of thefirst current.

The first current represents a current value corresponding to a highgrayscale data voltage, or the first current represents a current valueflowing to the organic light emitting diode when the organic lightemitting diode emits light with the maximum luminance.

The second current represents a current value corresponding to the lowgrayscale data voltage, or the second current represents a current valuethat is 0.1% to 50% of the first current.

The second voltage is compensated with a compensation voltage valuecaused by a difference between the second voltage and a voltage valueapplied to a gate electrode of the driving transistor that is detectedby sinking with a current value flowing to the organic light emittingdiode when the organic light emitting diode emits light with the minimumluminance.

The organic light emitting diode display further comprises: acompensator for receiving the first voltage and the second voltagethrough the data line; and a compensator selecting switch providedbetween the data line and the compensator, and transmitting the firstvoltage or the second voltage to the compensator when turned on by acorresponding selection signal.

The compensator comprises a first current sink for sinking the firstcurrent so as to detect the first voltage, and a second current sink forsinking the second current so as to detect the second voltage.

The compensator further comprises a controller for calculating athreshold voltage and an electron mobility of the driving transistoraccording to the first voltage and the second voltage, and determining acompensation amount of the data signal according to the calculatedthreshold voltage and electron mobility of the driving transistor.

Another embodiment of the present invention provides an organic lightemitting diode (OLED) display comprising: a plurality of pixelsincluding a plurality of organic light emitting diodes and a pluralityof driving transistors for supplying a driving current to the organiclight emitting diodes; a plurality of data lines for transmittingcorresponding data signals to the pixels; and a compensator forreceiving a plurality of first voltages and a plurality of secondvoltages that are respectively applied to the respective gate electrodesof the driving transistors through the data lines while sinking a firstcurrent and a second current on a path of a driving current from thedriving transistor to the organic light emitting diode through the dataline.

The compensator calculates a threshold voltages and an electron mobilityof the respective driving transistors according to the received firstvoltages and second voltages, and compensates the data signals that aretransmitted to the pixels according to the calculated threshold voltagesand electron mobility of the driving transistors.

The compensator receives driving voltages of the organic light emittingdiodes through the corresponding data lines while supplying apredetermined third current to the organic light emitting diodes throughthe data lines, determines deterioration degrees of the organic lightemitting diodes according to the received driving voltages, andcompensates the data signals that are transmitted to the pixelsaccording to the determined deterioration degrees.

The organic light emitting diode display further comprises a selectorincluding a plurality of data selecting switches connected to the datalines and a plurality of compensator selecting switches connected to anode of a plurality of diverged lines divided from the data lines.

The compensator selecting switches are turned on by the correspondingselection signals to transmit driving voltages of the organic lightemitting diodes to the compensator.

The compensator comprises a current source for supplying thepredetermined third current to the organic light emitting diodes.

The compensator further comprises a controller for determiningdeterioration degrees of the organic light emitting diodes according torespective driving voltages of the organic light emitting diodes, anddetermining a compensation amount of the data signal according to thedetermined deterioration degree.

Yet another embodiment of the present invention provides a method fordriving an organic light emitting diode (OLED) display comprising aplurality of pixels including a plurality of organic light emittingdiodes and a plurality of driving transistors for supplying a drivingcurrent to organic light emitting diodes, a plurality of data lines fortransmitting corresponding data signals to the pixels, and a compensatorfor receiving a plurality of first voltages and a plurality of secondvoltages that are applied to respective gate electrodes of the drivingtransistors through the data line while sinking a first current and asecond current on a path of driving current from the driving transistorto the organic light emitting diode through the data line.

The method comprises: receiving the first voltages and the secondvoltages applied to the respective gate electrodes of the drivingtransistors through the corresponding data line, thereby sensing avoltage; calculating a threshold voltage and an electron mobility of therespective driving transistors according to the received first voltagesand second voltages, thereby performing calculation; and compensating aplurality of data signals transmitted to the pixels according to thecalculated threshold voltages and electron mobility of the drivingtransistors.

The method for driving the organic light emitting diode display furthercomprises: receiving driving voltages of the organic light emittingdiodes while the compensator supplies a predetermined third current tothe organic light emitting diodes through the data lines, therebysensing a driving voltage; and determining deterioration degrees of theorganic light emitting diodes according to the received drivingvoltages, and compensating the data signals transmitted to the pixelsaccording to the determined deterioration degree, thereby performingcompensation.

While the sensing of a driving voltage is performed, the predeterminedthird current is controlled to flow to the organic light emitting diodesincluded in the pixels, and first transistors of the pixels fortransmitting the driving voltage of the organic light emitting diode tothe corresponding data line are turned on.

While the sensing of a voltage is performed, first transistors of thepixels connected between electrodes of the organic light emitting diodesand the corresponding data lines, driving transistors of the pixels forsupplying driving current to the organic light emitting diodes, andsecond transistors of the pixels connected between the correspondingdata line and a gate electrode of the driving transistor are turned on.

The method further comprises, before the calculation, compensating thesecond voltage with a compensation voltage value caused by a differencebetween the second voltage and a voltage value applied to a gateelectrode of a driving transistor detected by sinking with a currentvalue flowing to the organic light emitting diode when the organic lightemitting diode emits light with the minimum luminance.

According to an embodiment of the present invention, image quality isimproved by preventing non-uniformity and deviation of luminance causedby non-uniformity of a threshold voltage of transistors of pixels anddeviation of electron mobility in an organic light emitting diode (OLED)display.

Further, according to an embodiment of the present invention, a screencan be displayed with desired luminance in spite of deterioration of anorganic light emitting diode (OLED) in real-time, and by quicklydetecting deterioration of an organic light emitting diode included inthe pixels of an organic light emitting diode display and compensatingthe same. In addition, desired black luminance can be obtained byovercoming the problem of quickly sensing deterioration of an organiclight emitting diode and simultaneously realizing achievement of blackluminance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings, in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a block diagram of an organic light emitting diode (OLED)display according to an exemplary embodiment of the present invention;

FIG. 2 is a diagram showing a detailed part of configuration shown inFIG. 1;

FIG. 3 is a circuit diagram of a pixel shown in FIG. 1 according to anexemplary embodiment of the present invention;

FIG. 4 is a circuit diagram of a more detailed part of a configurationshown in FIG. 2 according to an exemplary embodiment of the presentinvention;

FIG. 5 to FIG. 8 are driving waveforms supplied to a pixel and aselector according to an exemplary embodiment of the present invention;

FIG. 9 is a driving waveform supplied to a pixel and a selectoraccording to another exemplary embodiment of the present invention;

FIG. 10 is a graph of current curves for grayscales in an organic lightemitting diode display to which an existing algorithm is applied; and

FIG. 11 is a graph of current curves for grayscales in an organic lightemitting diode display to which an algorithm according to an exemplaryembodiment of the present invention is applied.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

Constituent elements having the same structures throughout theembodiments are denoted by the same reference numerals and are describedin a first embodiment. In the other embodiments, only constituentelements other than the same constituent elements will be described.

In addition, parts not related to the description are omitted for cleardescription of the present invention, and like reference numeralsdesignate like elements and similar constituent elements throughout thespecification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. In addition, unlessexplicitly described to the contrary, the word “comprise” and variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

FIG. 1 is a block diagram of an organic light emitting diode (OLED)display according to an exemplary embodiment of the present invention.

The organic light emitting diode (OLED) display includes a display 10, ascan driver 20, a data driver 30, a sensing driver 40, a timingcontroller 50, a compensator 60, and a selector 70.

The display 10 includes a plurality of pixels 100 arranged thereon, andeach pixel 100 includes an organic light emitting diode (OLED) (refer toFIG. 3) for emitting light corresponding to a flow of driving currentaccording to a data signal transmitted from the data driver 30.

A plurality of scan lines S1, S2, . . . , Sn formed in the row directionand transmitting scan signals, a plurality of emission control linesEM1, EM2, . . . , EMn for transmitting light emission control signals,and a plurality of sensing lines SE1, SE2, . . . , SEn for transmittingsensing signals are formed on the pixels 100. Also, a plurality of datalines D1, D2, . . . , Dm arranged in a column direction and transmittingdata signals are formed on the pixels 100. The plurality of data linesD1, D2, . . . , Dm can selectively further transmit a driving voltage ofthe organic light emitting diode (OLED) caused by deterioration of theorganic light emitting diode included in the pixel, a threshold voltageof a driving transistor, and a voltage at a gate electrode of thedriving transistor for calculating mobility, in addition to thecorresponding data signals.

The display 10 receives a first power source voltage ELVDD and a secondpower source voltage ELVSS for supplying driving current to the pixelsfrom a power supply (not shown).

The scan driver 20 for applying the scan signals to the display 10 isconnected to the scan lines S1, S2, . . . , Sn and transmits the scansignals to the corresponding scan lines.

Also, the scan driver 20 for applying the light emission control signalsto the display 10 is connected to the emission control lines EM1, EM2, .. . , EMn, and transmits the light emission control signals to thecorresponding emission control lines.

The scan driver 20 is described in the exemplary embodiment of thepresent invention to generate and transmit the light emission controlsignals together with the scan signals, and the present invention is notlimited thereto. That is, a display device according to anotherexemplary embodiment of the present invention can additionally include alight emission control driver.

The sensing driver 40 for applying the sensing signals to the display 10is connected to the sensing lines SE1, SE2, . . . , SEn, and transmitsthe sensing signals to the corresponding sensing lines.

The data driver 30 for transmitting the data signals to the display 10receives the image data signals Data2 from the timing controller 50 togenerate a plurality of data signals, and transmits the data signals tothe corresponding data lines D1, D2, . . . , Dm in synchronization withthe time when the scan signals are transmitted to the corresponding scanlines. The data signals output by the data driver 30 are transmitted tothe pixels of one row to which the scan signal is transmitted among thepixels 100 of the display 10. The driving current following thecorresponding data signals flows to the organic light emitting diodes(OLEDs) of the pixels.

The compensator 60 detects a driving voltage of the plurality of organiclight emitting diodes (OLEDs) respectively included in the pixels,accordingly senses the deterioration (hereinafter, a deteriorationdegree) of the organic light emitting diodes (OLEDs), and determines adata signal compensation amount CA of compensating the senseddeterioration degree. Here, the data signal compensation amount CA isdetermined by the sensed deterioration degree and the data signal.

Also, the compensator 60 senses the voltages at the gate electrodes ofthe plurality of driving transistors included in the pixels, andrespectively calculates the threshold voltage and the mobility of thedriving transistors to compensate the deviation for the thresholdvoltage and the mobility of the driving transistors. The compensator 60determines the data signal compensation amount CA based on thecalculated threshold voltage and mobility of the driving transistors sothat the organic light emitting diode (OLED) may emit light with thetarget luminance corresponding to the data signal, in spite of thedeviation of the threshold voltage and mobility. The target luminanceoccurs when the current that is generated when the corresponding datasignal is transmitted to the driving transistor having the thresholdvoltage and the mobility set as a reference flows to the organic lightemitting diode (OLED).

The compensator 60 stores the data signal compensation amountsrespectively corresponding to the plurality of image data signals Data2for the respective organic light emitting diodes of the pixels. Thecompensator 60 transmits the data signal compensation amount CA to thetiming controller 50, and the timing controller 50 adds thecorresponding data signal compensation amount CA to the image datasignal corresponding to the image signal to generate the compensatedimage data signal.

The selector 70 includes a plurality of selecting switches (not shown,referred to as data selecting switches) connected to the data lines D1,D2, . . . , Dm, a plurality of selecting switches (not shown, referredto as compensator selecting switches) for connecting a plurality ofdiverged lines branched from the data lines D1, D2, . . . , Dm to thecompensator 60, and a selection driver 75 for generating andtransmitting a plurality of selection signals for controlling the dataselecting switches and the compensator selecting switches.

The data selecting switches transmit the data signals output by the datadriver 30 to the plurality of data lines during the period in which thedisplay device displays the images (hereinafter, referred to as an imagedisplay period). That is, the data selecting switches are turned onduring the image display period.

The compensator selecting switches respectively connect the data linesto the compensator 60 during a period for measuring the driving voltageof the organic light emitting diode (OLED) and a period for receivingthe gate voltages of the plurality of driving transistors to calculatethe characteristic deviation of the threshold voltage (hereinafter, asum of two periods will be referred to as a sensing period). Thecompensator selecting switches are turned off during the image displayperiod. Also, the compensator selecting switches are sequentially turnedon during the sensing period.

The selection driver 75 can receive the selection driving control signalSD from the timing controller 50 to generate a first selection signalfor controlling the switching operation of the plurality of dataselecting switches or a second selection signal for controlling theswitching operation of the plurality of compensator selecting switches.The selector 70 corresponding to the drive timing according to anexemplary embodiment of the present invention will be described indetail with reference to FIG. 4.

Since the data selecting switches are turned on by the plurality offirst selection signals during the image display period, the pixelsincluded in a predetermined pixel row among the plurality of pixels emitlight according to the driving current caused by the data signaltransmitted by the corresponding data lines.

During the sensing period, the compensator selecting switches aresequentially turned on by the second selection signals. While thesensing signals are transmitted to a predetermined pixel row via sensinglines SE1, SE2, . . . , SEn, the diverged lines branched from the datalines are connected to the compensator 60 through the compensatorselecting switches that are sequentially turned on. The pixels of thepixel row to which the sensing signal is transmitted are connected tothe compensator 60. The above-described operation is repeated for eachof the sensing lines SE1, SE2, . . . , SEn and the pixels of thecorresponding pixel row. Accordingly, information on the pixels 100 towhich the sensing signals are transmitted is transmitted to thecompensator 60 according to the corresponding second selection signal.Here, the information on each pixel includes the driving voltage of thecorresponding organic light emitting diode (OLED), the mobility, and thevoltage at the gate electrode of the corresponding driving transistor.

The timing controller 50 is connected to the scan driver 20, the datadriver 30, the sensing driver 40, and the selection driver 75 includedin the selector 70, and receives a video (image) signal Data1, asynchronizing signal SYNC, and a clock signal CLK to generate andtransmit control signals for controlling the scan driver 20, the datadriver 30, the sensing driver 40, and the selection driver 75 includedin the selector 70.

The timing controller 50 receives image signals Data1 (RGB imagesignals) including red, blue, and green, and generates image datasignals Data2 by using the data signal compensation amount CAtransmitted by the compensator 60.

Here, the timing controller 50 generates each image data signal byapplying the threshold voltage of the corresponding driving transistor,the mobility, and the data signal compensation amounts of compensatingthe deviation for the driving voltage of the corresponding organic lightemitting diode (OLED) to the image signal. The image data signals Data2are transmitted to the data driver 30, and the data driver 30 transmitsthe data signals according to the image data signals Data2 to the pixelsof the display 10. All pixels emit light by the threshold voltage of thecorresponding driving transistors, the deviation of mobility, and thecurrents of which deviation caused by deterioration of the correspondingorganic light emitting diodes (OLED) are compensated.

A partial configuration of the organic light emitting diode (OLED)display according to an exemplary embodiment of the present inventionwill be described in further detail with reference to FIG. 2.

FIG. 2 is a diagram showing a partial configuration including thecompensator from among the configuration of the organic light emittingdiode (OLED) display of FIG. 1.

Referring to FIG. 2, the compensator 60 is connected to the timingcontroller 50 and the selector 70, and the selector 70 connects the datadriver 30 to the pixel 100 and the compensator 60.

The pixel 100 shown in FIG. 2 represents one corresponding pixel fromamong all pixels configuring the display 10, and the compensationprocess and drive of the compensator 60, timing controller 50, selector70, and the data driver 30 included in the organic light emitting diode(OLED) display according to an exemplary embodiment of the presentinvention are performed for all pixels of the display 10.

The compensator 60 includes a current source 601, a first current sink603, a second current sink 605, an analog-to-digital converter (ADC)607, a memory 609 having a lookup table 611, and a controller 613.

One current source 601, one first current sink 603, and one secondcurrent sink 605 are shown in FIG. 2, however it is not limited thereto,and more than one current source 601, first current sink 603, and secondcurrent sink 605 may be provided.

In a like manner in FIG. 2, one analog-to-digital converter 607connected to the current source 601, the first current sink 603, and thesecond current sink 605 is shown, however a plurality ofanalog-to-digital converters 607 that are respectively connected to aplurality of current sources 601, a plurality of the first current sinks603, and a plurality of the second current sinks 605, or are connectedinto a group, may be provided.

When a corresponding compensator selecting switch from among a pluralityof compensator selecting switches is turned on during the sensingperiod, the current source 601 supplies a first current I₁ to theorganic light emitting diode (OLED) of the corresponding pixel 100during a period in which a switch included in the current source 601 isturned on.

A driving voltage (a first voltage) of the organic light emitting diode(OLED) of the pixel 100 is supplied to the analog-to-digital converter607 through the corresponding data line connected to the pixel 100.Here, the first current is supplied through the organic light emittingdiode (OLED) included in the pixel 100. Therefore, the first voltagesupplied to the analog-to-digital converter 607 can have a voltage valuehaving reflected deterioration of the organic light emitting diode(OLED).

In detail, as the organic light emitting diode (OLED) included in thepixel 100 is deteriorated, resistance of the organic light emittingdiode (OLED) is increased, and a voltage value at an anode of theorganic light emitting diode (OLED) is increased. A current value of thefirst current is experimentally determined so that a predeterminedvoltage may be applied, and when an expected voltage value of theorganic light emitting diode (OLED), when the first current is supplied,is changed to a voltage value, that is, the first voltage, that isincreased by deterioration of the organic light emitting diode (OLED),the change is sensed by controller 613, as will be explained later. Thevoltage value corresponding to a difference between the expected voltagevalue of the organic light emitting diode (OLED) for the first currentand the voltage value of the first voltage indicates deterioration ofthe organic light emitting diode (OLED).

Detection of the driving voltage of the organic light emitting diode(OLED) of the pixel 100 performed by the current source 601 is performedat all pixels of the display 10 in response to turn-on of a plurality ofcompensator selecting switches, and respective first voltages of allpixels are transmitted to the analog-to-digital converter 607 during thesensing period.

When a corresponding compensator selecting switch from among a pluralityof compensator selecting switches is turned on during the sensingperiod, the first current sink 603 sinks the second current I₂ to thecorresponding pixel 100 from among a plurality of pixels while a switchincluded in the first current sink 603 is turned on. The second currentis sunk by passing through the driving transistor included in the pixel100. The voltage (a second voltage) at the gate electrode of the drivingtransistor is transmitted through a corresponding data line connected tothe pixel 100 from among a plurality of data lines. A threshold voltageand mobility of the driving transistor of the pixel 100 can becalculated by using the second voltage. Detailed calculation of thethreshold voltage and mobility of the driving transistor using thesecond voltage will be described later with reference to FIG. 4.

The current value of the second current can be set variously so that apredetermined voltage may be applied within a predetermined time, and itcan be particularly set as a current value corresponding to a highgrayscale data voltage. Desirably, it can be set to be a current value(Imax) that will flow to the organic light emitting diode (OLED) whenthe pixel 100 emits light with the maximum luminance.

Detection of the second voltage of the driving transistor of the pixel100 performed by the first current sink 603 is performed at all pixelsof the display 10 in response to turn-on of a plurality of compensatorselecting switches, and respective second voltages of the entire pixelsare detected and transmitted to the analog-to-digital converter 607during the sensing period.

When a corresponding compensator selecting switch from among a pluralityof compensator selecting switches is turned on during the sensingperiod, the second current sink 605 sinks the third current I₃ to thecorresponding pixel 100 from among a plurality of pixels while a switchincluded in the second current sink 605 is turned on. The third currentis sunk by passing through the driving transistor included in the pixel100. A voltage (a third voltage) at the gate electrode of the drivingtransistor is transmitted to the analog-to-digital converter 607 througha data line connected to the pixel 100 from among a plurality of datalines. In a like manner, the threshold voltage and mobility of thedriving transistor of the pixel 100 can be calculated by using the thirdvoltage.

Here, the third current I₃ is set to be less than the second current I₂.Particularly, the third current can be set to correspond to the lowgrayscale data voltage.

In the exemplary embodiment, the third current may be determined as acurrent value of 0.1% to 50% of the second current.

In another exemplary embodiment, the third current can be a current thatcorresponds to ¼ of the current value (Imax) that will flow to theorganic light emitting diode (OLED) when the pixel 100 emits light withthe maximum luminance.

In the exemplary embodiment, the third voltage of the pixel 100 that issensed when the current is sunk by the third current sink can becompensated by using the difference with the voltage value of the gateelectrode of the driving transistor of the pixel that is detected whensunk with the current value corresponding to the minimum grayscale datavoltage, and can be used to calculate the threshold voltage and themobility of the driving transistor, in order to overcome the drawbackthat is generated when the current is sunk with a current as low as thecurrent value corresponding to the minimum grayscale data voltage and tomaintain the merit.

That is, when the current is sunk with the current value correspondingto the minimum grayscale data voltage, the time for charging the voltageat the gate electrode of the driving transistor of the pixel 100 intothe corresponding data line is relatively long, and hence it isdifficult to quickly sense the voltage in real-time. When the current issunk with a low current value, it is difficult to realize it in ahardwired manner and generate it without deviation. However, when it issunk with the current value corresponding to the grayscale data voltage,black luminance of a desired level can be acquired and the low grayscaledata are easily realized.

Therefore, the organic light emitting diode (OLED) display sets thethird current with a current value that is greater than the currentvalue corresponding to the minimum grayscale data voltage, and sensesthe third voltage within a short time to easily compensate data inreal-time. However, it accordingly becomes difficult to achieve blackluminance, which is compensated by finding a compensated voltage valuecaused by a difference with the third voltage based on the voltage ofthe driving transistor that is sensed when the current is sunk by thecurrent value that corresponds to the minimum grayscale data voltage.

Detection of the third voltage of the driving transistor of the pixel100 performed by the second current sink 605 is detected at all pixelsof the display 10 in response to turn-on of a plurality of compensatorselecting switches, and the third voltages of the entire pixels aredetected and transmitted to the analog-to-digital converter 607 duringthe sensing period.

During the sensing period, the second voltage and the third voltagesensed from each of a plurality of pixels are used to find thresholdvoltages and electron mobility of the driving transistors included in aplurality of pixels.

The analog-to-digital converter 607 converts the first voltage, thesecond voltage, and the third voltage that are respectively sensed fromthe entire pixels of the display 10 and respectively supplied from thecurrent source 601, the first current sink 603, and the second currentsink 605 into digital values.

Also, referring to FIG. 2, the compensator 60 includes a memory 609 anda controller 613.

The memory 609 stores the digital values of the first voltage, thesecond voltage, and the third voltages transmitted by theanalog-to-digital converter 607.

The controller 613 calculates the threshold voltages and the mobilitydeviation of the driving transistors and the deterioration degree of theplurality of organic light emitting diodes (OLED) by using the digitalinformation on the first voltage, the second voltage, and the thirdvoltage sensed for the pixels. The memory 609 stores the calculatedthreshold voltages and mobility deviation of the driving transistors anddeterioration degrees of the organic light emitting diodes (OLEDs).

As described, the memory 609 stores the threshold voltages and themobility deviation of the driving transistors of the pixels, and thedeterioration degrees of the organic light emitting diodes (OLEDs) perpixel.

The controller 613 calculates a data signal compensation amount CA ofcompensating the image data signals Data2 according to the calculatedthreshold voltage and the mobility of the driving transistors, and thedeterioration degrees of the organic light emitting diodes (OLEDs). Thememory 609 can store the data signal compensation amount as a lookuptable 611. Here, the lookup table 611 stores the data signalcompensation amount of compensating the image data signals Data2, thecalculated threshold voltage and the mobility of the driving transistor,and the deterioration degree deviation of the organic light emittingdiode (OLED), or it can store an expression for calculating the datasignal compensation amount.

The timing controller 50 transmits the image data signal Data1 of apredetermined bit b₁ for representing the grayscale of an arbitrarypixel in the video signal to the controller 613. The controller 613detects the information on the threshold voltage of the drivingtransistor, the mobility deviation, and the deterioration of the organiclight emitting diode (OLED) from the memory 609, and reads the datasignal compensation amount CA for compensating the image data signaltransmitted according to the detected deviation and deterioration degreefrom the lookup table 611.

The controller 613 transmits the data signal compensation amount CA tothe timing controller 50, and the timing controller 50 adds the datasignal compensation amount CA to the image data signal Data1 to generatea corrected image data signal Data2 and transmit it to the data driver30.

In detail, the image data signal Data1 can be the digital signal inwhich 8-bit digital signals representing the grayscale of one pixel arecontinuously arranged. The timing controller 50 can add the data signalcompensation amount CA corresponding to the 8-bit digital signal togenerate a digital signal of different bits, for example a 10-bitdigital signal. The corrected image data signal Data2 becomes the signalin which the 10-bit digital signal is continuously arranged.

Upon receiving the corrected image data signal Data2, the data driver 30uses the same to generate the data signal, and supplies the generateddata signal to the pixels 100 of the display 10. The image sticking iscompensated and the factor for the mura phenomenon is removed from thepixels, thereby displaying the image in uniform luminance.

FIG. 3 is a circuit diagram of a pixel shown in FIG. 1 according to anexemplary embodiment.

FIG. 3 is a circuit diagram of a pixel 100 at a position thatcorresponds to an n-th pixel row and an m-th pixel column from among aplurality of pixels included in the display 10 shown in FIG. 1.

The pixel 100 includes an organic light emitting diode (OLED), a drivingtransistor M1, a first transistor M3, a second transistor M2, a thirdtransistor M4, and a storage capacitor Cst.

The pixel 100 includes an organic light emitting diode (OLED) foremitting light according to a driving current I_(D) applied to theanode, the driving transistor M1 transmitting the driving current I_(D)to the organic light emitting diode (OLED).

The driving transistor M, provided between the anode of the organiclight emitting diode (OLED) and the first power source voltage ELVDD,controls current flowing from the first power source voltage ELVDD tothe second power source voltage ELVSS through the organic light emittingdiode (OLED).

In detail, a gate of the driving transistor M1 is connected at node N1to a first end of the storage capacitor Cst, and a first electrodethereof is connected at node N4 to a second end of the storage capacitorCst and the first power source voltage ELVDD. The driving transistor M1controls the driving current I_(D) flowing to the organic light emittingdiode (OLED) from the first power source voltage ELVDD corresponding tothe voltage value according to the data signal stored in the storagecapacitor Cst. In this instance, the organic light emitting diode (OLED)emits light corresponding to the driving current supplied by the drivingtransistor M1.

The first transistor M3, provided between nodes N3 and N2, i.e., theanode of the organic light emitting diode (OLED) and a data line Dm,respectively, receives a driving voltage of the organic light emittingdiode (OLED) from the organic light emitting diode (OLED).

In detail, a gate of the first transistor M3 is connected to the sensingline SEn connected to the pixel 100, the first electrode is connected atnode N1 to the anode of the organic light emitting diode (OLED), and thesecond electrode is connected at node N2 to the data line Dm. The firsttransistor M3 is turned on when the sensing signal of a gate on voltagelevel is supplied to the sensing line SEn, and it is turned off in othercases. The sensing signal is supplied during the sensing period.

The second transistor M2 is connected to the scan line Sn connected tothe pixel 100 and the data line Dm connected to the pixel 100, andtransmits the data signal of data line Dm to the driving transistor M1in response to the scan signal transmitted by the scan line Sn.

In detail, a gate of the second transistor M2 is connected to the scanline Sn, the first electrode is connected at node N2 to thecorresponding data line Dm, and the second electrode is connected atnode N1 to the gate of the driving transistor M1. The second transistorM2 is turned on when the scan signal of a gate on voltage level issupplied to the scan line Sn, and it is turned off in other cases. Thescan signal has an on voltage level when the voltage at the gateelectrode of the driving transistor M1 is sensed in the compensator 60from among the sensing period and when a predetermined data signal istransmitted from the data line Dm.

The third transistor M4 is provided between the anode of the organiclight emitting diode (OLED) and the driving transistor M1. A gateelectrode of third transistor M4 is connected to the emission controlline EMn connected to the pixel 100, and controls light emission of theorganic light emitting diode (OLED) in response to the light emissioncontrol signal transmitted by the emission control line EMn.

In detail, a gate electrode of the third transistor M4 is connected tothe corresponding emission control line EMn, a first electrode thereofis connected at node N5 to the second electrode of the drivingtransistor M1, and a second electrode thereof is connected at node N3 tothe anode of the organic light emitting diode (OLED). The thirdtransistor M4 is turned on when a light emission control signal of agate on voltage level is supplied to the emission control line EMn, andit is turned off in other cases.

The storage capacitor Cst has a first end connected at node N1 to thegate electrode of the driving transistor M1 and a second end connectedat node N4 to the first electrode of the driving transistor M1 and thefirst power source voltage ELVDD.

A voltage V_(th) corresponding to the threshold voltage of the drivingtransistor M1 is charged in the storage capacitor Cst, and when the datasignal is transmitted from the data line Dm, a voltage at first node N1where the first end of the storage capacitor Cst and the gate electrodeof the driving transistor meet is changed corresponding to the datasignal. When the driving transistor M1 and the third transistor M4 areturned on to form a current path from the first power source voltageELVDD to the cathode of the organic light emitting diode (OLED), thecurrent corresponding to the voltage that corresponds to the differencebetween the voltage value Vgs of the driving transistor M1, that is, thevoltage of the data signal that is applied to the gate electrode of thedriving transistor M1 and the power source voltage ELVDD at the firstelectrode is applied to the organic light emitting diode (OLED), and theorganic light emitting diode (OLED) emits light corresponding to theapplied current.

FIG. 4 is a circuit diagram of a more detailed part of a configurationshown in FIG. 2 according to an exemplary embodiment of the presentinvention.

In detail, FIG. 4 shows a connection of a more detailed configuration ofthe current source 601 and the current sinks 603 and 605 of thecompensator 60 of FIG. 2; a detailed configuration of a portion of theselector 70 of FIG. 1; and the circuit diagram of the pixel 100 of FIG.3. The pixel 100 of FIG. 4 represents one corresponding pixel from amongall pixels configuring the display 10, and the compensation process anddriving by the compensator 60, the timing controller 50, the selector70, and the data driver included in the organic light emitting diode(OLED) display according to an exemplary embodiment of the presentinvention are performed for all pixels of the display 10.

A process for compensating image sticking and mura phenomenon in anorganic light emitting diode (OLED) display by using waveform diagramsof FIG. 5 to FIG. 9 together with FIG. 4 according to an exemplaryembodiment of the present invention will now be described.

FIG. 4 shows a data selecting switch SW1 and compensator selectingswitch SWm connected to the data line Dm connected to the pixel 100 fromamong a plurality of data selecting switches and a plurality ofcompensator selecting switches of the selector 70.

The compensator selecting switch SWm is connected to a diverged linebranched from the data line Dm connected to the pixel 100. In thisinstance, the diverged line branched from the data line represents acompensation line 73.

When the compensator selecting switch SWm is turned on during thesensing period, the pixel 100 is sensed through the compensation line 73and the data line Dm by the compensator selecting switch SWm. Thecurrent source 601, the first current sink 603, and the second currentsink 605 of the compensator 60 are connected to the compensation line 73connected to the corresponding data line Dm.

The current source 601 includes a first switch SW2, and is controlled bythe switching operation of the first switch SW2. The first current sink603 includes a second switch SW3, and is controlled by the second switchSW3. Also, the second current sink 605 includes a third switch SW4, andis controlled by the third switch SW4. The selection signals forcontrolling the switching operations of the first switch SW2, the secondswitch SW3, and the third switch SW4 can be generated and transmitted bythe timing controller 50 or by the selection driver 75 of the selector70.

The first switch SW2, the second switch SW3, and the third switch SW4can be commonly connected to one node, and the voltage at the node istransmitted to the analog-to-digital converter 607.

FIG. 5 is a waveform diagram for the first current sink 603 to sense thesecond voltage, FIG. 6 is a waveform diagram for the second current sink605 to sense the third voltage, FIG. 7 is a waveform diagram for thecurrent source 601 of the compensator 60 to sense the first voltage,FIG. 8 is a waveform diagram for transmitting a data signal anddisplaying an image at the pixel 100, and FIG. 9 is a driving waveformof an organic light emitting diode (OLED) display according to anotherexemplary embodiment of the present invention, showing a waveformdiagram for transmitting the data signal to the pixel 100 and displayingthe image when simultaneously sensing the first voltage.

The waveform diagrams shown in FIG. 5 to FIG. 9 are proposed for thecase in which transistors and a plurality of selecting switches forconfiguring the circuit of the pixel 100 shown in FIG. 4 are PMOStransistors, and when the transistors and a plurality of selectingswitches included in the circuit of the pixel 100 are realized with NMOStransistors, the polarity of the waveform diagrams will be reversed.

It will be sufficient when the process for compensating the imagesticking and mura phenomenon before the display 10 of the organic lightemitting diode (OLED) displays an image in the exemplary embodiment ofthe present invention, and the respective compensation processes are notrestricted to the order of FIG. 5 to FIG. 9. Compensation can beperformed at a predetermined time that is automatically determined, andit can be performed at a time established by the user.

A process for the organic light emitting diode (OLED) display shown inFIG. 4 according to an exemplary embodiment of the present invention tosense a voltage at the gate electrode of the driving transistor M1 ofthe pixel 100 according to the waveform of FIG. 5 will now be described.

Referring to FIG. 5, at the time t1, the data selection signal SWC1 forcontrolling the data selecting switch SW1 connected to the data linecorresponding to the pixel 100 is transmitted as the high level at whichthe data selecting switch SW1 is turned off. Since the compensatorselection signal SWCm is transmitted as the low level at the time t1,the compensator selecting switch SWm connected to the compensation line73 divided from the data line corresponding to the pixel 100 is turnedon.

A scan signal S, a light emission control signal EM, and a sensingsignal SE that are supplied to the pixel 100 are transmitted as a lowlevel voltage at the time t1. Accordingly, in the pixel 100 of FIG. 4,the second transistor M2 having received the scan signal S, the thirdtransistor M4 having received the light emission control signal EM, andthe first transistor M3 having received the sensing signal SE are turnedon at the time t1.

During the period P1 in which the second transistor M2, the thirdtransistor M4, and the first transistor M3 are turned on, the secondswitch SW3 of the first current sink 603 is turned on by the low-levelselection signal SWC3. The second current is sunk through the data lineconnected through the turned-on compensator selecting switch SWm duringthis period.

Accordingly, the driving transistor M1 is turned on to form the currentpath from the first power source voltage ELVDD to the cathode of theorganic light emitting diode (OLED). Also, the voltage difference Vgsbetween the gate electrode of the driving transistor M1 and the firstelectrode is formed as the voltage value corresponding to the secondcurrent, and the voltage (the second voltage) at the gate electrode ofthe driving transistor M1 is applied to the first node N1.

The second voltage is transmitted to the analog-to-digital converter 607passing through the data line Dm connected to the pixel 100 through thesecond transistor M2, and the compensation line 73, and is convertedinto the digital value.

Referring to FIG. 6, from the time t3 to the time t4, the data selectionsignal SWC1 for controlling the data selecting switch SW1 is transmittedas high level and the data selecting switch SW1 is turned off. On thecontrary, since the compensator selection signal SWCm is transmitted aslow level at the time t3, the compensator selecting switch SWm connectedto the compensation line 73 divided from the data line corresponding tothe pixel 100 is turned on.

At the time t3, the scan signal S, the light emission control signal EM,and the sensing signal SE supplied to the pixel 100 are transmitted aslow level voltages to turn on the second transistor M2, the thirdtransistor M4, and the first transistor M3 during the period P2.

Here, the third switch SW4 of the second current sink 605 is turned onin response to the low-level selection signal SWC4. The second currentsink 605 sinks the third current through the data line connected throughthe turned-on compensator selecting switch SWm during the period P2.

Accordingly, the driving transistor M1 is turned on to form the currentpath from the first power source voltage ELVDD to the cathode of theorganic light emitting diode (OLED). Also, the voltage difference Vgsbetween the gate electrode of the driving transistor M1 and the firstelectrode is formed as the voltage value corresponding to the thirdcurrent such and the voltage (the third voltage) at the gate electrodeof the driving transistor M1 is applied to the first node N1.

The third voltage is passed through the data line Dm connected to thepixel 100 through the second transistor M2 and the compensation line 73,is transmitted to the analog-to-digital converter 607, and is convertedinto the digital value.

The memory 609 of the compensator 60 stores digital values of theconverted second voltage and the third voltage, and the controller 613calculates the threshold voltage and the electron mobility of thedriving transistor M1 of the pixel 100 from the voltage values.

As an exemplary embodiment, a current value of the second current sunkby the first current sink 603 is set to be the current value Imax whenthe pixel emits light with the maximum luminance, and a current value ofthe third current sunk by the second current sink 605 is set to be acurrent value corresponding to the low grayscale data voltage, andparticularly it is set to be the current value ¼ Imax that correspondsto ¼ of Imax.

A voltage value at the gate electrode of the driving transistor M1applied to the first node N1 of FIG. 4 when the current is sunk with thesecond current and the third current, that is, the voltage value V1 ofthe second voltage and the voltage value V2 of the third voltage, arecalculated as follows.

$\begin{matrix}{{V\; 1} = {{E\; L\; V\; D\; D} - \sqrt{\frac{2\;{I\max}}{\beta}} - {{{VthM}\; 1}}}} & {{Equation}\mspace{14mu} 1} \\{{V\; 2} = {{E\; L\; V\; D\; D} - {\frac{1}{2}\sqrt{\frac{2\;{I\max}}{\beta}}} - {{{VthM}\; 1}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Here, ELVDD of Equations 1 and 2 is the voltage value supplied by thefirst power source voltage ELVDD and it is the voltage at the firstelectrode of the driving transistor M1 at node N4.

Also, β is the mobility of the electrons moving in the channel of thedriving transistor M1, and |VthM1| is a proper threshold voltage of thedriving transistor M1 of the pixel 100.

Hence, the threshold voltage and mobility of the driving transistor M1in the two equations can be found.

However, when the current is sunk with the third current that is set tobe the current value ¼ Imax, it is difficult to realize the lowgrayscale data. Particularly, since it is difficult to achieve blackluminance with a desired level, a predetermined compensation voltagevalue (Vshift) is applied to the voltage value V2 of the third voltagethat is detected when sunk by the third current. The detection time ofthe third voltage becomes faster and achievement of black luminance of adesired level is enabled since the current is not sunk with the minimumcurrent. When the compensation voltage value (Vshift) is applied,Equation 3 is acquired.

$\begin{matrix}\begin{matrix}{{V\; 3} = {{V\; 2} + {Vshift}}} \\{= {{E\; L\; V\; D\; D} - {\frac{1}{2}\sqrt{\frac{2\;{I\max}}{\beta}}} - {{{VthM}\; 1}} + {Vshift}}}\end{matrix} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Here, the V3 voltage value represents the voltage value applied to thefirst node N1 when the pixel 100 is sunk with the current value that isgiven when the pixel 100 emits light with the lowest luminance. When theentire grayscale is 256 grayscale levels, it indicates the voltage valuethat is detected when the current is sunk with the current value of1/256 Imax.

Unknown quantities Q1 and Q2 relating to the mobility and thresholdvoltage of the driving transistor are calculated by using Equations 1and 3, and the threshold voltage and mobility of the driving transistorM1 included in a plurality of pixels of the display 10 can becalculated.

The unknown quantities Q1 and Q2 are expressed in Equations 4 and 5.

$\begin{matrix}{{Q\; 1} = \sqrt{\frac{2\;{I\max}}{\beta}}} & {{Equation}\mspace{14mu} 4} \\{{Q\; 2} = {{{{VthM}\; 1}} = {{E\; L\; V\; D\; D} - {Q\; 1} - {V\; 1}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

The threshold voltage and mobility of the driving transistor M1 for therespective pixels calculated by the controller 613 are stored in thememory 609.

The waveform diagram of FIG. 7 is the waveform diagram of the period inwhich the driving voltage of the organic light emitting diode (OLED) ofthe pixel 100 is sensed.

Referring to FIG. 7, during the period P3 from the time t5 to the timet6, the data selection signal SWC1 is transmitted as high level to turnoff the data selecting switch SW1, and the compensator selection signalSWCm is low-level, and hence the compensator selecting switch SWmconnected to the compensation line 73 divided from the data linecorresponding to the pixel 100 is turned on.

During the period P3, the scan signal S and the light emission controlsignal EM are transmitted as a high level voltage, and the sensingsignal SE is transmitted as a low level voltage.

Accordingly, the second transistor M2 having received the scan signal Sand the third transistor M4 having received the light emission controlsignal EM in the pixel 100 are turned off during the period P3, and thefirst transistor M3 having received the sensing signal SE is turned onduring the period P3.

Here, the first switch SW2 of the current source 601 receives thelow-level selection signal SWC2, and is turned on in response thereto.The current source 601 supplies the first current to the organic lightemitting diode (OLED) through the compensation line 73 and the data lineDm connected through the turned-on compensator selecting switch SWmduring period P3.

In the case of a normal organic light emitting diode (OLED), the drivingvoltage applied to the anode is the appropriate voltage valuecorresponding to the first current, however resistance of thedeteriorated organic light emitting diode (OLED) is increased torelatively increase the driving voltage applied to the anode of theorganic light emitting diode (OLED). The increased driving voltage ofthe organic light emitting diode (OLED) is the first voltage, and thefirst voltage is transmitted to the analog-to-digital converter 607passing through the turned-on first transistor M3, the data line Dm, andthe compensation line 73, and is converted into a digital value.

The memory 609 stores the digital value of the first voltage, and thecontroller 613 determines the data signal compensation amount ofcompensating by the voltage value increased by the deterioration basedon the first voltage so that the organic light emitting diode (OLED) mayemit light with appropriate luminance according to the data signal.

FIG. 8 is a waveform diagram for the pixel 100 to normally emit lightaccording to the data signal.

From the time t7 to the time t8, the data selection signal SWC1 is lowlevel, and the data selecting switch SW1 connected to the data linecorresponding to the pixel 100 is turned on in response thereto. On thecontrary, since the compensator selection signal SWCm is transmitted ashigh level during the period of the time t7 to time t8, the compensatorselecting switch SWm connected to the compensation line 73 divided fromthe data line corresponding to the pixel 100 is turned off.

The low-level scan signal S is supplied to the pixel 100 at the time t7,and the second transistor M2 is turned on during the period P4.

The data driver 30 transmits the compensated data signal to thecorresponding data line Dm through the turned-on data selecting switchSW1 during the period P4. The data signal is transmitted to the firstnode N1 passing through the second transistor M2, and the storagecapacitor Cst connected to the first node N1 charges the voltage valuecorresponding to the data signal.

The data signal transmitted to the pixel 100 is generated from the imagedata signal corrected by the timing controller 50 of FIG. 4.

The corrected image data signals Data2 are converted into an analog datasignal by a digital analog converter 31 of the data driver 30.

The analog data signal can be supplied to the data line Dm connected tothe corresponding pixel 100 from among a plurality of pixels through anegative feedback type operational amplifier 33. Since the organic lightemitting diode (OLED) of the pixel 100 emits light according to thecorrected data signal, image sticking and mura phenomenon are removedfrom the entire image of the display 10 to provide quality images.

FIG. 9 is a waveform diagram of a process for sensing in real-time thedriving voltage of the organic light emitting diode (OLED) when normallydriving the display according to another exemplary embodiment of thepresent invention.

Referring to FIG. 9, since the compensator selection signal SWCm fallsto become low level at the time t9 and maintains the low level duringthe period P5, the compensator selecting switch SWm connected to thecompensation line 73 divided from the data line corresponding to thepixel 100 is turned on during the period P5. Since the compensatorselection signal SWCm rises to become the high level at the time t10,the compensator selecting switch SWm is turned off during the period P6.On the contrary, the data selection signal SWC1 is transmitted as highlevel during the period P5 to turn off the data selecting switch SW1,and the data selection signal SWC1 is transmitted as low level duringthe period P6 to turn on the data selecting switch SW1.

The sensing signal SE supplied to the pixel 100 is a low level voltageat the time t9 and it is supplied during the period P5, turning firsttransistor M3 on. During the period P5, the first switch SW2 of thecurrent source 601 is turned on in response to the selection signalSWC2.

During the period P5, in a like manner of the method described withreference to FIG. 7, the current source 601 supplies the first currentto the organic light emitting diode (OLED) through the data line and thecompensation line 73 connected through the turned on compensatorselecting switch SWm, and transmits the first voltage to theanalog-to-digital converter 607 through the turned on first transistorM3.

The first switch SW2 is turned off in response to the selection signalSWC2 at the time t10, and the data selection signal SWC1 simultaneouslyfalls to become low level to turn on the data selecting switch SW1during the period P6.

Since the low-level scan signal S is supplied to the pixel 100 at thetime t10, the second transistor M2 is turned on during the period P6.The data signal is transmitted to the first node N1 by passing throughthe second transistor M2 through the corresponding data line Dm in alike manner of the method described with reference to FIG. 8, during theperiod P6, and the storage capacitor Cst is charged with the voltagevalue according to the corresponding data signal.

When the scan signal S rises to a high level voltage at the time t11after the storage capacitor Cst is charged with the voltagecorresponding to the data signal, the second transistor M2 is turnedoff, and the light emission control signal EM falls to the low levelvoltage to turn on the third transistor M4. Therefore, the drivingtransistor M1 supplies the driving current corresponding to the datasignal to the organic light emitting diode (OLED) to display an imagewith predetermined luminance.

In the waveform diagram of FIG. 9, the corresponding sensing signal SEis supplied before the scan signal S corresponding to the pixel 100 issupplied to store driving voltage information of the organic lightemitting diode (OLED) in the memory 609. During a predetermined oneframe period, the driving voltage of the organic light emitting diode(OLED) is sensed and is stored in the memory 609, and the corrected datasignal is transmitted to the pixel in the next frame period to emitlight.

FIG. 10 is a graph of current curves for grayscales of the organic lightemitting diode (OLED) display having applied the existing algorithm.

In detail, FIG. 10 shows a graph of current curves for grayscales of theimage of which the data signal is corrected by detecting the voltage atthe gate electrode of the driving transistor of the pixel following thewaveform diagrams of FIG. 5 and FIG. 6, and finding and compensating thethreshold voltage and mobility deviation of the driving transistor andby using Equations 1 and 2.

It is found in FIG. 10 that the pixel having emitted light according tothe compensated data signal failed to sufficiently realize the lowgrayscale data area.

However, when the compensation amount is calculated by applying acompensation voltage value (Vshift) for compensating the difference withthe voltage value of the gate electrode of the driving transistor of thepixel that is detected by sinking the current with the current valuecorresponding to the minimum grayscale data voltage, it is found asshown in FIG. 11 that the low grayscale data area is sufficientlyexpressed in correspondence to the 2.2 gamma curve.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. Also, the material of respectiveconstituent elements described in the specification can be easilyselected and substituted from various materials by a person of ordinaryskill in the art. Furthermore, a person of ordinary skill in the art canomit part of the constituent elements described in the specificationwithout deterioration of performance or can add constituent elements forbetter performance. In addition, a person of ordinary skill in the artcan change the specification depending on the process conditions orequipment. Hence, the range of the present invention is to be determinedby the claims and equivalents.

What is claimed is:
 1. An organic light emitting diode display having aplurality of pixels, each pixel comprising: an organic light emittingdiode (OLED); a driving transistor for supplying a driving current tothe organic light emitting diode; a data line for transmitting acorresponding data signal to the driving transistor; a first transistorhaving a first electrode connected to one electrode of the organic lightemitting diode and a second electrode connected to the data line; and asecond transistor having a first electrode connected to the data lineand a second electrode connected to a gate electrode of the drivingtransistor: wherein the first transistor, the second transistor, and thedriving transistor are turned on, a first current and a second currentare respectively sunk in a path of a driving current from the drivingtransistor to the organic light emitting diode through the data line,and wherein a threshold voltage and an electron mobility of the drivingtransistor are calculated by receiving a first voltage and a secondvoltage applied to the gate electrode of the driving transistorcorresponding to sinking of the first current and the second currentthrough the second transistor and the data line, and the data signaltransmitted to the data line is compensated.
 2. The organic lightemitting diode display of claim 1, wherein the display receives a thirdvoltage applied to one electrode of the organic light emitting diodethrough the data line while supplying a predetermined third current tothe organic light emitting diode by turning on the first transistor, andthe display detects a deterioration degree of the organic light emittingdiode according to the third voltage, and compensates a data signaltransmitted to the data line in order to compensate the detecteddeterioration.
 3. The organic light emitting diode display of claim 2,further comprising: a compensator for receiving the third voltagethrough the data line; and a compensator selecting switch providedbetween the data line and the compensator, and transmitting the thirdvoltage to the compensator when turned on by a corresponding selectionsignal.
 4. The organic light emitting diode display of claim 3, whereinthe compensator comprises a current source for supplying a third currentso as to detect the third voltage.
 5. The organic light emitting diodedisplay of claim 4, wherein the compensator further comprises acontroller for determining a deterioration degree of the organic lightemitting diode according to the third voltage, and determining acompensation amount corresponding to a data signal according to thedetermined deterioration degree.
 6. The organic light emitting diodedisplay of claim 1, wherein the second current has a current value thatis less than that of the first current.
 7. The organic light emittingdiode display of claim 6, wherein the first current represents a currentvalue corresponding to a high gray scale data voltage.
 8. The organiclight emitting diode display of claim 6, wherein the first currentrepresents a current value flowing to the organic light emitting diodewhen the organic light emitting diode emits light with the maximumluminance.
 9. The organic light emitting diode display of claim 6,wherein the second current represents a current value corresponding tothe low gray scale data voltage.
 10. The organic light emitting diodedisplay of claim 6, wherein the second current represents a currentvalue that is 0.1% to 50% of the first current.
 11. The organic lightemitting diode display of claim 1, wherein the second voltage iscompensated with a compensation voltage value caused by a differencebetween the second voltage and a voltage value applied to a gateelectrode of the driving transistor that is detected by sinking with acurrent value flowing to the organic light emitting diode when theorganic light emitting diode emits light with the minimum luminance. 12.The organic light emitting diode display of claim 1, further comprising:a compensator for receiving the first voltage and the second voltagethrough the data line; and a compensator selecting switch providedbetween the data line and the compensator, and transmitting the firstvoltage or the second voltage to the compensator when turned on by acorresponding selection signal.
 13. The organic light emitting diodedisplay of claim 12, wherein the compensator comprises: a first currentsink for sinking the first current so as to detect the first voltage;and a second current sink for sinking the second current so as to detectthe second voltage.
 14. The organic light emitting diode display ofclaim 13, wherein the compensator further comprises a controller forcalculating a threshold voltage and an electron mobility of the drivingtransistor according to the first voltage and the second voltage, anddetermining a compensation amount corresponding to the data signalaccording to the calculated threshold voltage and electron mobility ofthe driving transistor.
 15. An organic light emitting diode display,comprising: a plurality of pixels including a plurality of organic lightemitting diodes and a plurality of driving transistors for supplyingdriving current to the organic light emitting diodes; a plurality ofdata lines for transmitting corresponding data signals to the pixels;and a compensator for receiving a plurality of first voltages and aplurality of second voltages that are respectively applied to therespective gate electrodes of the driving transistors through the datalines while respectively sinking the first current and the secondcurrent on a path of a driving current from the driving transistor tothe organic light emitting diode through the data line; wherein thecompensator calculates a threshold voltages and an electron mobility ofthe respective driving transistors according to the received firstvoltages and second voltages, and compensates the data signals that aretransmitted to the pixels according to the calculated threshold voltagesand electron mobility of the driving transistors.
 16. The organic lightemitting diode display of claim 15, wherein the compensator receivesdriving voltages of the organic light emitting diodes through thecorresponding data lines while supplying a predetermined third currentto the organic light emitting diodes through the data lines, determinesdeterioration degrees of the organic light emitting diodes according tothe received driving voltages, and compensates the data signals that aretransmitted to the pixels according to the determined deteriorationdegrees.
 17. The organic light emitting diode display of claim 16,wherein the organic light emitting diode display further comprises aselector including a plurality of data selecting switches connected tothe data lines and a plurality of compensator selecting switchesconnected to a node of a plurality of diverged lines divided from thedata lines, and the compensator selecting switches are turned on by thecorresponding selection signals to transmit driving voltages of theorganic light emitting diodes to the compensator.
 18. The organic lightemitting diode display of claim 16, wherein the compensator comprises acurrent source for supplying the predetermined third current to theorganic light emitting diodes.
 19. The organic light emitting diodedisplay of claim 18, wherein the compensator further comprises acontroller for determining deterioration degrees of the organic lightemitting diodes according to respective driving voltages of the organiclight emitting diodes, and determining a compensation amount of the datasignal according to the determined deterioration degree.
 20. The organiclight emitting diode display of claim 15, wherein the second current hasa current value that is less than that of the first current.
 21. Theorganic light emitting diode display of claim 20, wherein the firstcurrent represents a current value that corresponds to a high gray scaledata voltage.
 22. The organic light emitting diode display of claim 20,wherein the first current represents a current value flowing to theorganic light emitting diode when the organic light emitting diode emitslight with the maximum luminance.
 23. The organic light emitting diodedisplay of claim 20, wherein the second current represents a currentvalue that corresponds to a low gray scale data voltage.
 24. The organiclight emitting diode display of claim 20, wherein the second current hasa current value that is 0.1% to 50% of the current value of the firstcurrent.
 25. The organic light emitting diode display of claim 15,wherein the second voltage is compensated with a compensation voltagevalue caused by a difference between the second voltage and a voltagevalue that is applied to the gate electrode of the driving transistorthat is detecting by sinking with a current value flowing to the organiclight emitting diode when the organic light emitting diode emits lightwith the minimum luminance.
 26. The organic light emitting diode displayof claim 15, wherein the compensator comprises: a first current sink forsinking the first current in order to detect the first voltages; and asecond current sink for sinking the second current in order to detectthe second voltages.
 27. The organic light emitting diode display ofclaim 26, wherein the compensator further comprises a controller forcalculating threshold voltages and electron mobility of the respectivedriving transistors according to the first voltages and the secondvoltages, and determining a compensation amount corresponding to therespective data signals that are transmitted to the pixels according tothe calculated threshold voltages and electron mobility of the drivingtransistors.
 28. The organic light emitting diode display of claim 15,wherein the organic light emitting diode display further comprises aselector including a plurality of data selecting switches connected tothe data lines and a plurality of compensator selecting switchesconnected to a node of a plurality of diverged lines divided from thedata lines, and the compensator selecting switches are turned on bycorresponding selection signals to transmit the first voltages and thesecond voltages to the compensator.
 29. A method for driving an organiclight emitting diode (OLED) display comprising a plurality of pixelsincluding a plurality of organic light emitting diodes and a pluralityof driving transistors for supplying a driving current to organic lightemitting diodes, a plurality of data lines for transmittingcorresponding data signals to the pixels, and a compensator forreceiving a plurality of first voltages and a plurality of secondvoltages that are applied to respective gate electrodes of the drivingtransistors through the data line while sinking a first current and asecond current on a path of a driving current from the drivingtransistor to the organic light emitting diode through the data line,the method comprising the steps of: receiving the first voltages and thesecond voltages applied to the respective gate electrodes of the drivingtransistors through the corresponding data line, thereby sensing avoltage; calculating a threshold voltage and an electron mobility of therespective driving transistors according to the received first voltagesand second voltages, thereby performing calculation; and compensating aplurality of data signals transmitted to the pixels according to thecalculated threshold voltages and electron mobility of the drivingtransistors.
 30. The method of claim 29, wherein the method for drivingthe organic light emitting diode display further comprises: receivingdriving voltages of the organic light emitting diodes while thecompensator supplies a predetermined third current to the organic lightemitting diodes through the data lines, thereby sensing a drivingvoltage; and determining deterioration degrees of the organic lightemitting diodes according to the received driving voltages, andcompensating the data signals transmitted to the pixels according to thedetermined deterioration degree, thereby performing compensation. 31.The method of claim 30, wherein while the sensing of a driving voltageis performed, the predetermined third current is controlled to flow tothe organic light emitting diodes included in the pixels, and firsttransistors of the pixels for transmitting the driving voltage of theorganic light emitting diode to the corresponding data line are turnedon.
 32. The method of claim 29, wherein while the sensing of a voltageis performed, first transistors of the pixels connected between oneelectrodes of the organic light emitting diodes and the correspondingdata lines, driving transistors of the pixels for supplying drivingcurrent to the organic light emitting diodes, and second transistors ofthe pixels connected between the corresponding data line and a gateelectrode of the driving transistor are turned on.
 33. The method ofclaim 29, wherein the second current has a current value that is lessthan the first current.
 34. The method of claim 33, wherein the firstcurrent represents a current value that corresponds to a high gray scaledata voltage.
 35. The method of claim 33, wherein the first currentrepresents a current value flowing to the organic light emitting diodewhen the organic light emitting diode emits light with the maximumluminance.
 36. The method of claim 33, wherein the second currentrepresents a current value that corresponds to a low gray scale datavoltage.
 37. The method of claim 33, wherein the second current has acurrent value that is 0.1% to 50% of the current value of the firstcurrent.
 38. The method of claim 29, further comprising the step of,before the calculation, compensating the second voltage with a voltagevalue applied to a gate electrode of the driving transistor detectedwhen sinking with a current value corresponding to a difference of acurrent value shifted in a low gray scale data voltage.
 39. The methodof claim 29, further comprising the step of, before the calculation,compensating the second voltage with a compensation voltage value causedby a difference between the second voltage and a voltage value appliedto a gate electrode of a driving transistor detected by sinking with acurrent value flowing to the organic light emitting diode when theorganic light emitting diode emits light with the minimum luminance.